Ni–Sn coatings as cathodes for hydrogen evolution in alkaline solution. Chemical composition, phase composition and morphology effects

In this work the hydrogen evolution reaction (HER) onto Ni–Sn alloy coatings deposited at different current densities from the bath containing 0.1 M Sn2+ and 0.1 M Ni2+ ions in the pyrophosphate–glycine solution, was investigated by polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Their morphology and chemical composition were investigated by scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDS), while the phase composition was investigated by X-ray powder diffraction (XRPD). It was shown that their chemical composition, phase composition and morphology depend on the deposition current density. In deposited samples all detected phases, face centered cubic (fcc) Ni, close packed (hcp) hexagonal Ni3Sn, hexagonal Ni(1+x)Sn (0 < x < 0.5) which adopts NiAs structure type and monoclinic Ni3Sn4 (CoSn structure type), were of low crystallinity. The increase of the Ni–Sn alloy coatings catalytic activity for HER in 6 M KOH with increasing the deposition current density was shown to be the consequence of the change of all three parameters: chemical composition, phase composition and morphology, with the effect of morphology being the most pronounced.